1. Field of the Invention
The present invention relates to a scroll type compressor having a pair of scroll type compression units mounted in a single casing and also to a refrigeration cycle incorporating such a scroll type compressor.
2. Description of the Related Art
A refrigeration cycle has been proposed which includes a plurality of compressors encased in independent casings, with the compressors being selectively operated such that one, two or more of these compressors operate simultaneously to enable control of refrigeration power in accordance with a change in the refrigeration demand. It has also been proposed to use combinations of at least one compressor having a large compression power and at least one compressor having a small compression power, so as to enable a delicate control of the refrigeration power over a wider range. A promblem arises in the use of a plurality of compressors in various combinations with regard to sufficient lubrication of the compressors. This problem is serious particularly when the independent compressors have their own lubricating oil reservoirs in their casings. Namely, in such a case, lubricating oil tends to be shifted from one compressor to another compressor during running of the refrigeration cycle, so as to cause a shortage of oil in one compressor while the other is charged with excessive oil. Various specific measures have to be taken to maintain optimum oil levels in all the compressors for a long time.
In order to overcome this problem, it has been proposed to incorporate a plurality of compression units in a single casing having a lubricating oil reservoir which is common to all these compression units.
This type of compressor having a plurality of compression units having a common oil reservoir formed in a single casing, however, suffers from a disadvantage that alteration of the capacity of the compressor essentially requires alteration of constructions and specifications of the compressor units encased in the single casing. Since different types of compression units are employed, as well as differing combinations of these compression units, enormous cost is incurred not only in the production and service but also in administration of the component parts.